I disagree because I know I am going to marry my boyfriend, I am very serious about that, but I have decided to stop having sex with him because I know that it is against what I believe religiously.

Just because he made a mistake out of passion does not mean that he does not love her or take her seriously. Maybe now he simply wants to enjoy them as friends (they've only been dating a couple of months) and allow their love for each other to blossom.

This way, when they marry (because it sounds to me like he might be heading that direction) they will enjoy the sex more because neither will be regretful.

Seeing it from his perspective